Facebook's newest feature, Nearby Friends, begins rolling out today -- sadly for Americans only, to begin with. The opt-in feature broadcasts your exact location, and can even give real-time updates as you move around, if that's the kind of thing you want to share with your friends.
Making its way to Facebook's Android and iOS app in the coming weeks, Nearby Friends thankfully works by reciprocal opt-in: you can only see friends' proximity if you allow yourself to be visible on Nearby Friends, and you'll only be able to request someone's precise map location by first offering yours to them. And Nearby Friends will have the same multi-mode privacy options as your newsfeed, allowing you to limit Nearby Friends updates to all, some, or none of your friends.
The precise location feature allows you and a selected friend to view exact map locations for a set period of time, probably to help you and your friend find each other in a crowd. After that set time expires, you're back to standard mode, where you're alerted when friends are close but not shown their exact map locations.
When Nearby Friends rolls out (assuming they roll it out outside of the US, and you turn it on) you'll see a list showing the friends that are geographically closest to you who've opted in to the feature. The list includes distance away in mile increments, time of last location update, and in bigger metropolitan areas, the name of the neighborhood your friend is in. From the list, a button next to each friend will allow you to share and request exact map locations with a 40 character message, and set how long you'll be visible to them (minutes, hours, or until manually shut off). The GPS-powered feature will use your phone's accelerometers and shut off when you're stationary to try and minimise battery draw.
Facebook is following what's now become its standard practice, making this new feature a separate navigation app rather than folding it into an update to the main Facebook app. It's also a pretty direct shot at other location-based social media offerings from the likes of Foursquare, not to mention the long-forgotten Google Latitude.